Archive for the ‘Iowa Barn Owl Research’ Category

POST RELEASE SURVIVAL AND MOVEMENTS OF CAPTIVELY
REARED COMMON BARN-OWLS IN IOWA

Bruce L. Ehresman, Douglas A. Reeves, and Kerry P. Schlarbaum

Iowa Department of Natural Resources
Wildlife Research Station
RR #1, Ledges Road
Boone IA 50036
ABSTRACT
From 1983 through 1987, 427 common barn-owls (Tyto alba pratincola) were captively reared and gently released in Iowa. Owls were released from 44 sites in 28 counties where grassland habitat appeared suitable. Numbers of verified barn-owl sightings reported to DNR personnel increased steadily during the project period from 17 in 1983 to 48 in 1986, probably due to greater public awareness about barn-owls brought on by information related to the releases. Numbers of confirmed or suspected nestings of barn-owls in Iowa varied from zero to 5 per year during the study period. No banded (released) individuals were known to contribute to any of the nestings. Thirty-six common barn-owls were equipped with radio transmitters and released during 1985 and 1986. Twenty-four perished before radio contact was lost, two were unmonitored because they escaped the radio harness, and 10 were known alive 30 or more days post-release. It does not appear that wild barn-owls have become significantly more numerous in Iowa because of releases of captively reared owls. Our emphasis now is on placing nest boxes in quality habitat areas where barn-owls are sighted, and increasing awareness of the barn-owl’s value through public education.
INTRODUCTION
The common barn-owl (Tyto alba pratincola) is a widespread resident of the United States. In southern and coastal portions of this country it is still considered common. However, in the Midwest and northern reaches of its range it has become increasingly rare during the last 30 years. In fact the barn-owl is listed as endangered or threatened in at least 7 Midwestern states. In Iowa, it has been listed as endangered since 1977 (14). This means the barn-owl is likely to disappear as a nesting species in the state if it declines further in numbers.
REASONS FOR DECLINE
Decline of the barn-owl can probably be attributed to a combination of factors. These include grassland destruction, loss of nesting and roosting sites, severe winter weather, predation, collision mortality, and possible pesticide effects (5,8,11,12,17). Marked changes in land use patterns have perhaps had particularly devastating effects in Iowa. Crop rotations which included about 25 percent meadow in the 1950’s are now replaced by two-year rotations of corn and soybeans throughout much of the state. As crop fields are enlarged, brushy fencerows, vacant buildings, woodlots and idle areas are eliminated which previously provided barn-owls nest and roost sites as well as foraging areas.
INITIATION OF RESTORATION PROJECT
An extensive literature review and discussions with raptor specialists provided initial support for the proposal of a project to enhance numbers of barn-owls in Iowa by releasing captively produced birds. Field inspections of habitat around known nest sites of native barn-owls, together with information on regional land use patterns further supported the notion that suitable unoccupied habitat existed in Iowa in at least the southern portion of the state. This information, together with the fact that barn-owls breed readily in captivity, gave Iowa Conservation Commission’s Nongame Wildlife personnel cause to begin a captive breeding and restoration program.
BARN-OWL PLACEMENT
Beginning in 1982, 93 barn-owls, both wild and captively produced, were acquired by the Iowa Conservation Commission (now the DNR or Department of Natural Resources) from rehabilitation centers and zoos in Washington, Oregon, California, Arizona, Texas, Louisiana, South Carolina, and Illinois. These were then used for captive breeding at the Boone Wildlife Research Station (WRS) facilities or placed at selected release sites. At the WRS rearing facility, adult owls were paired and placed in individual pens where they nested and reared their own young. More detailed information about housing, diet, etc. is recorded by Ehresman (8).
In order to place and release barn-owls, support and cooperation of landowners throughout Iowa was enlisted to assist with the project. The DNR publicly advertised a need for release sites, and the response was very good. Nearly 200 concerned citizens responded by offering their farmsteads as potential release sites. Landowners were sent a standardized form to complete and return so nongame staff could evaluate their sites. Foremost in the analysis was the amount of grassland in the form of hayfields, idle areas, wet meadows, and pastures that each potential release site contained. Other barn-owl studies indicate that suitable foraging habitat may be the most important factor for barn-owl reproduction (1,4). Also, b providing nest boxes in conjunction with foraging habitat, we hoped to document nesting of released owls. Many of the release sites chosen were later found to be in areas where barn-owls had previously existed.
Once release sites were chosen, the barns, silos, or out-buildings where the owls would be held were prepared. Olefin fiber netting was placed over openings to keep owls in and predators out, and a nest box was placed in the structure. To increase chances of documenting barn-owl nesting post-0release, other nest boxes were placed in the vicinity of the release site in nearby structures. Owl pairs from the Boone facility were usually placed at release sites during January and February. Release site attendants (usually landowners) then cared for the owls until they nested and reared offspring successfully. In many cases additional owlets of similar age from the Boone facility were added to these nests. Once the young owls were capable of sustained flight, the netting was removed from an opening in the building, and all owls (usually 7 or were allowed to come and go at will. All owls released were banded with US F&WS aluminum lock on bands. During 1985, 1986, and 1987, numbered colored plastic leg bands were attached as well. Colors used were red, blue, and yellow respectively. Release site attendants continued to feed the owls after release as long as the owls remained at the site (usually 2 to 4 days).
Besides placing barn-owl pairs at release sites, two other methods of placement were implemented. This included placing pairs from the Boone facility with their 3 to 4 week-old young. The final method involved placing groups of 5 to 7 barn-owls (usually fledglings) that were reared by captive pairs at the Boone facility or received as nestlings from other states. Normally owls placed by one of the latter methods were only held at release sites for 4 to 6 weeks prior to release. Release techniques for all 3 methods were the same.
From 1983 through 1987, 427 barn-owls were released from 44 sites in 28 Iowa counties (Table 1). Overall, 73 adult owls and 354 juveniles were released. Release areas chosen were primarily in the southern counties (Fig. 1), where most of Iowa’s remaining grassland exists. However, several release areas were chosen in northeast Iowa where most of Iowa’s dairy farming occurs, and in the Loess Hills of western Iowa, where there is some remnant native prairie.
After 2 years of releasing barn-owls. It was evident that the birds were not returning to release sites to nest. Aside from a limited number of sightings of barn-owls at or near release sites within 2 year post-release, there was no other evidence to suggest survival or nesting. To remedy this lack of information, barn-owl telemetry studies were implemented in 1985 and 1986 to gather knowledge about survival, movements, and habitat use of captively produced barn-owls released into the wild.
STUDY AREAS
Two different areas were selected for the telemetry studies. In 1985, two release sites were chosen near Chariton, Iowa, in Lucas County (Fig 2). The gently rolling topography in this southern Iowa location included a mixture of pasture, hayfields, idle grassland, row crops, and patchy timber. This area seemed favorable for barn-owl habitation, since barn-owls had been documented in the vicinity prior to owl releases.
The three release sites used in 1986 were further north than the 1985 release sites but still in the southern half of the state. Two sites were located east of Tama in southern Tama County, and the third site was located south of Chelsea in northern Poweshiek County (Fig. 2). The topography and habitat for two of the release sites was similar to those of 1985. The third site was located in the Otter Creek Marsh Wildlife Management Area (WMA). This site was selected because of predominant wet meadow and emergent wetland habitats which have been found in other barn-owl studies (2,4) to be important barn-owl foraging areas. It was also theorized that there would be fewer great horned owls (Bubo virginianus) in this bottomland habitat to prey on the barn-owls.
RADIOING BARN-OWLS
During January 1985, a pair of adult barn-owls was placed in each of 2 barns near Chariton, Iowa (Fig. 2). The owls were provided with a nest box and confined to the barn until they had mated, nested, and reared a brood to fledging. After the juvenile owls were flying well in the barn, backpack-mounted radio transmitters were attached to all of the owls using 1/8 inch diameter elastic shock cord. The transmitters were Telonics RB-5 models and weighed 27 grams. All birds were confined in the barn for 1 week after they were equipped with transmitters to assure that they could fly acceptably and had adjusted to the transmitters, a luxury that many wildlife telemetry studies do not have. One complicating factor was that the adults in the barn near Williamson (northern site) had already re-nested when the first brood was ready to be released. The first brood of young was released without accompanying adults. Later, the adults and the second brood were released. In all, 17 barn-owls were equipped with transmitters and released in 1985.
In 1986 a pair of adult owls was placed at each of 2 locations east of Tama. Each pair produced young, and the releases were handled in the same manner as the 1985 releases. In addition, 3 seven months-old and 2 two year old barn-owls produced at the Boone WRS were placed at a barn in the Otter Creek Marsh WMA, equipped with transmitters, and released. A total of 19 owls was equipped with transmitters and released during 1986. Smaller Telonics MOD-040* transmitter packages, weighing 18 grams, were used during the 1986 field study. They were attached using backpack mounts. In 1985, 5 radioed owls were released on June 26, 7 on July 3, and 5 on August 20. In 1986, 6 radioed owls were released August 19, 8 on August 27, and 5 on September 26.
 
RADIO-TRACKING BARN-OWLS
Equipment used to locate radioed owls included a car-mounted dual yagi antenna connected to a programmable Advanced Telemetry Systems* (ATS) receiver. Most locations were made with this vehicle-tracking system. Single element antennae were used when locating owls at close range (retrieving mortality victims or finding owls on roosts) and from aircraft when owls could not be located from the ground.
Owl locations were determined by triangulation using two or more signal readings taken from different locations. Whenever possible, right-angle comparison readings were made to specify the exact location. Compass bearings of each signal coordinate readings, as determined from the directional antenna readings, were recorded for each session and the points were plotted on a study area map. Locations were then recorded on a data sheet as Universal Transverse Mercator (UTM) coordinates to the nearest 100 meter grid (1 hectare). Using the vehicle-tracking system, radio transmitter signals had a range of 2 to 11 kilometers.
Radio locations of the owls were taken every night as often as possible during 1985, and daytime roosts were documented. In 1986, a main priority was to determine nightly activity patterns of individual owls, so some owls were monitored only every second or third day. As in 1985, locations were made mostly at night, and daytime roosts were noted. Efforts were made to determine the specific location of transmitters whose location had not changed appreciably after a 2 to 3 day period. Mortalities were noted and the probable cause of death was recorded.
BARN-OWL MOVEMENT
Barn-owls varied significantly in their response to release. At the Chariton release site most birds left eh barn during the first or second night. At one of the Tame release sites the birds stayed in or very close to the barn for 30 days. This created some difficulties with monitoring owl dispersal and survival, especially since the signal from some radios began to fade within 30 days, and most of the radios had ceased to function at the end of 45 days. The owls finally did disperse after food was no longer supplied for them in the barn, and they were forced to forage on their own. For most owls, once they had left the immediate release site, a pattern of movement did become apparent. After a short period (generally less than 4 days), they occupied identifiable home ranges that they then used for extended periods (up to 2 ½ months). Measuring to the geometric center of the home range, the mean distance travelled from a release site to a home range was 5.3 km for 7 birds that survived in excess of 30 days. During 1985, the 4 of 5 owls that lived more than 50 days following release then made extensive wide ranging movements during September. Unfortunately, because the smaller transmitters did not function as long during 1986, it could not be determined if the “surviving” owls made similar movements at the same number of days following release.
Several juvenile barn-owls travelled long distances during the study, and the direction of their movements following release appeared to be random (Fig. 3). In 1985, two birds travelled 48 km and 120 km northwest respectively; another flew 64 km northeast, and the fourth bird traveled 32 km in a southeasterly direction. In October 1986, 1 owl flew 40 km northeast before slipping its transmitter. Two owls that did make extensive movements were subsequently recovered. Both were killed in collisions with automobiles, one 48 km from the release site, the other 19 km from the release site after travelling to a distance of 64 km 2 months previously.
Random movements are not unusual for young barn-owls. Steward (17) termed these movements “post-natal wandering.” He noted that dispersal occurred in all directions during the first year out of the nest, and “of the 236 birds for which the places of recovery were determined, 63.7 percent were taken within 50 miles of the hatching places, and 34.3 percent were taken more than 50 miles distant.”
Band returns recorded for barn-owls (wild and captively reared) in Iowa from 1981-87 further support the fact that some barn-owls disperse to great distance (Fig. 4). The best evidence of this is a barn-owl banded as a nestling in southwest Iowa in 1981. In 1982 this owls was found dead 419 km away in extreme southeast Iowa were it had been the parent of 3 nestlings. All 7 owls that dispersed moved in an easterly direction 49 km to 419 km from where they were banded. This is inconsistent with Stewart’s (17) band return data which indicated more random directional movement.
MORTALITY
Twenty-four of 36 (67%) barn-owls perished before radio contact with them was lost. Stewart (17) found that 65.2% of first year birds do not survive. Two of the 36 radioed owls were not monitored because they slipped out of the transmitter harness within 2 days after release. “Surviving” owls are defined as birds that were still alive when radio contact was lost at least 30 days following release. Ten of 36 (28%) fit this category. Causes of mortality were assigned as follows:
1. Avian predation was attributed to barn-owl remains where either:
a. An avian predator was flushed from the carcass;
b. The remains were scattered over an area directly beneath a tree, and whitewash was found at the site, or;
c. The remains were picked clean, and bones and feathers were not chewed.
2. Probable mammalian predation was indicated when remains were found accompanied by scats of mammals, or when bones and feathers had been chewed; the owl had been dead too long to determine the cause of death.
3. Auto collision mortalities were found near roadways, and subsequent investigation indicated that severe trauma attributed to a collision resulted in the death of the bird.
4. Unknown deaths were those which could not reliably be assigned an obvious cause.
Great horned owls preyed on barn-owls. Several other authors have noted this (2,4,11,19), but not as frequently as we experienced. At least 9 of 24 37.5%) barn-owl deaths were attributed to great horned owl predation, and 4 other avian caused deaths may have been great horned owl casualties. Overall, 13 of 24 (54.2%) barn-owl deaths were caused by avian predation. Great horned owls were flushed from barn-owl carcasses, and it appeared that at one release site, the great horned owls became accustomed to catching and killing barn-owls., since they caught at least 4 of the birds within .5 km of the release site. All 4 were fledglings from the second brood radioed at a release site. Two owls were killed by great horned owls after the first release at this site also. It is known that great horned owls kill “wild” barn-owls in Iowa too. In 1985, a fledgling barn-owl was consumed by a great horned owl after it left its barn cupola nest in Clarke County (Beth Brown, pers. comm.). In an owl pellet study done in eastern Washington, it was found that “common barn-owls are the fourth most important prey item, in terms of total prey biomass, in the diet of great horned owls” (11). If fledgling barn-owls are in fact a normal item in the diet of great horned owls, there may be little chance of barn-owls becoming abundant where great horned owls occur in Iowa.
Although the extent of predation by great horned owls was greater than expected, it was not surprising to find that auto collisions accounted for 4 of 24 (16.7%) radioed barn-owl deaths. Past records of barn-owl deaths in Iowa (8), indicate that vehicle collisions do take their toll on barn-owls. Other studies have documented barn-owl collision mortality as well (10,15,16). In California, Schulz (15) indicated collisions with vehicles may be the major mortality factor in that state. During the telemetry study, numerous barn-owls were documented spending time along grassy roadside ditches. These areas are probably preferred hunting areas because adjacent fence posts supply low perches from which to hunt, and the ditches harbor an abundance of rodent prey. At least twice during the field studies a barn-owl was seen flying low across a roadway and was barely missed by a moving vehicle.
Two of 24 (8.3%) barn-owl mortalities were probably mammalian predation victims, and 5 (20.8%) owls were found dead of unknown causes (Table 2). Mammalian predation occasionally is documented on wild barn-owls (2). Of the 5 owls found dead of unknown causes, it is probably that 2 dies of starvation at the release sites.
Mortality was greatest during the first 20 days post-release. Chi-square analysis indicated that this was statistically significant (P < .01) for the two years pooled as well as for both individual years. Upon further investigation it was discovered that, with one exception, all know avian predation occurred during the first 20 days following release. Mortality after 20 days was attributed to probable mammalian predation, unknown causes, or auto collisions. This was interpreted to indicate a learned avoidance response to major predators (particularly) great horned owls) following an initial encounter.
Because of differences in the behavior of owls during the 2 years, and because of differences in the longevity of radio transmitters, it is difficult to make direct comparisons of the mortality information for the two years. One reason the mortality patterns appear different for the two years could be the differences in the weight of the radio transmitters. It is known that transmitter weight can affect avian survival (7.18). However, 5 birds wearing the heavier transmitters did survive for at least 55 days, and this same radio package was used by Ault (1) in a study of wild barn-owls in Oklahoma without negative impact. In Ault’s study, the radioed owls were carrying cotton rats (Sigmodon hispidus) (2nd most important food item) to the nests with no apparent transmitter-related problems. Cotton rats’ weight usually averages 115 grams (3), which was about 25 percent of the weight of many of the owls.
Another different in survival between years can be explained by the fact that 5 of 6 owls at one 1986 release site essentially stayed in the barn or close proximity to it for 30 days following “release,” and as a result were not subjected to the same mortality factors that the other owls were during the same time interval. In fact, 2 of the owls were never located more than 1 km from the barn before radio contact was lost. Barn-owls released at other sites usually moved away from the site within 1 week. Another factor that undoubtedly explains some of the apparent difference in mortality patterns between the 2 years is the longevity of the radio transmitters. Complete information was recorded for the owls during 1985 to beyond 40 days. During 1986, contact was lost with 4 owls during the 21-40 day interval. If those birds could have been followed for a longer period, a different mortality pattern might have been indicated.
Barn-owl mortality causes have also been documented from the 1983-87 barn-owls released in the form of band returns. To date, only 16 of 427 (3.8%) barn-owls released have yielded band returns. Of these 16, 5 died of apparent starvation, 4 were vehicle collision victims, 4 died of unknown causes, and 3 died of “other” causes. Three of the five owls which apparently starved did so because of severe weather conditions. One owl was found dead after it had been raining for 10 of 14 days, and the owl may have been unable to hunt effectively during that period. Two owls were found dead in Wisconsin in January following severe cold coupled with deep snow. Starvation of barn-owls during winter is not uncommon since many barn-owls do not migrate south (8,9,13). Of the 3 owls which died of “other” causes; 1 was bitten by a dog, 1 was killed when a grain auger was activated (the bird was roosting inside), and the third owl died of apparent heat exposure after being chased by other barn-owls in a building during hot weather.
BARN-OWL SIGHTINGS
Although the mortality documented by the telemetry studies paints a grim picture for survival of captively reared barn-owls in Iowa, there is evidence to indicate that barn-owls continue to exist here. Prior to 1983, it was unusual to document more than 4 barn-owl sightings in a year, and from 1950-1979, Dinsmore, et al (6) recorded only 7 nests. During the 5 years of barn-owl releases, 1983-87, a total of 171 barn-owl sightings were verified, 7 barn-owl nests were confirmed, and 7 possible or probable nestings were reported.
We hoped that by placing colored leg bands on released owls, the owls would be more visible and more sightings would result. However, there have been only 3 subsequent sightings of banded birds. These owls were observed alive at distances of 4.0, 5.6, and 11.3 km from the nearest release sites for 3-8 months following release.
Of the 171 verified sightings, (Fig. 5), 80 (46.8%) were of owls seen within 12.8 km of release sites, and 9 of those 80 were owls seen at release sites. One of the 9 owls seen at a release site was known to be a wild owl. The other 8 may have been captively reared birds.
Even though there have not been documented nestings of banded barn-owls, it is probable that some released owls do return to their natal site. Stewart (17) documented 65.7 percent of barn-owls banded at hatching sites were later found within 50 miles of these places. Because of these findings he felt “it is reasonably certain that some birds remain to nest in the general locality of their hatching places.” Bruce Colvin (unpublished) has documented in a New Jersey study area that among 49 adult birds handled in 1987, 5 (10.2%) of those were banded as chicks in the study area. And those 5 were among 870 young banded from 1980-86. Colvin’s 1986 data (unpublished) indicated 16.9 percent of the adult population were banded as nestlings on the study area.
Another factor that may have influenced the large number of reported barn-owl sightings near release sites could be increased public awareness that the DNR was interested in these sightings. Most releases involved newspaper coverage, and in some cases, television coverage. This resulted in a better informed public, particularly in release site areas, who were probably more likely to report barn-owl sightings than in areas where publicity did not occur.
 
BARN-OWL NESTING
Seven barn-owl nests were verified during the study period. Five of them were documented in 4 southern Iowa counties (Fig. 6), and the other 2 were at the same site in northwest Iowa (Sac County) for 2 consecutive years. Five adults were observed well enough at 3 sites to determine they were unbanded; no banded adults were sighted at active nest sites. Even though no banded birds have been seen at nest sites, one of the last locations made on a surviving radioed barn-owl in 1985 was just across the road from a site were barn-owls nested successfully in 1986.
CONCLUSION
Captive bred barn-owls have been documented nesting at release sites in Missouri and Nebraska. The release of over 200 barn-owls in a localized area of Missouri did result in at least 2 active nests involving released birds the following year (Walter Crawford, pers. Comm..). Nebraska Nongame Biologist, John Dinan (pers. Comm..) reported from 1 to 5 pairs of barn-owls nested at or near release sites following the release of over 150 barn-owls in a southeastern Nebraska area. It was unknown if any of the nesting owls in Nebraska were release birds, however.
There have been over 1,000 captive-reared barn-owls released in Iowa, Missouri, and Nebraska in the last 6 years (Crawford, Dinan, pers. comm.). Even with this large number of owls introduced into the wild, there is still not much evidence that these releases have had a significant positive biological impact on the Midwest barn-owl population.
The positive impact that has resulted from the releases (at least in Iowa) has been an increased public awareness of barn-owls. Educating the public about barn-owls is an important part of the Iowa DNR barn-owl restoration program. More people are now reporting barn-owl sightings, because they realize they are seeing something special. The Iowa DNR will no longer be releasing captive-bred barn-owls. Public education emphasis will continue, as will the placement of barn-owl nest boxes in areas where barn-owls are known to occur.
We do not feel that the captive-release program has been a failure. We have learned much about Iowa barn-owls which will be channeled into management of barn-owls to ensure their future in Iowa and the Midwest.
ACKNOWLEDGEMENTS
A special thanks is extended to all the folks who helped with this project. Without the hundreds of hours of volunteer time put in by these cooperators, the success of the restoration effort would not be realized. Thanks also to Rita Knight and Sandy Monen for typing this manuscript and to Mariene Ehresman for her editing efforts.
 

REFERENCES
1. Ault, J. W. III. A quantitative estimate of barn owl nesting habitat quality. M.S. Thesis, Oklahoma State University. 1982.
2. Bunn, D. S., A. B. Warburton and R. D. S. Wilson. The barn owl. Buteo Books, Vermillion, S.D. 264 pp. 1982.
3. Byrd, C. L. The home range, habitat, and prey utilization of barn owl (Tyto alba) in south Texas. M.S. Thesis. Texas A&I University, Kingsville. 88 pp. 1982.
4. Colvin, B. A. Barn owl foraging behavior and secondary poisoning hazard from rodenticide use on farms. Docotoral Diss. Bowling Green State Univ., OH. 326 pp. 1984.
5. ________. Common barn-owl population decline in Ohio and the relationship to agricultural trends. J. Field Ornithol. 56:224-235. 1985
6. Dinsmore, J. J. et al. Iowa birds, Iowa state University Press. Ames, Iowa. 356 pp. 1984.
7. Dunstan, T. C. A harness for radio-tagging raptorial birds. Inl. Bird-Banding News 44 (1): 4-8. 1972 in Schemnitz, S.D. Wildlife management techniques manual, 4th ed. The Wildlife Society, Washington, D.C. 686 pp. 1980.
8. Ehresman, B. L. Common barn-owl restoration in Iowa. Wildlife Rehabilitation. Pro. Nat. Wild. Rehab. Symp. Vol. 3:10-19. 1984.
9. Errington, P. L. Winter killing of barn owls in Wisconsin. Wilson Bull. 43:60. 1931.
10. Glue, D. E. Ringing recovery circumstances of small birds of prey. Bird Study 18:137-146. 1971. In Bunn et al. The barn owl. Buteo Books, Vermillion, S.D. 264 pp. 1982.
11. Knight, R. L. and R. E. Jackson. Food-niche relationships between great horned owls and common barn-owls in eastern Washington. Auk 101:175-179. 1984.
12. Lavcock, G. Dark days for barn-owls. Audubon 87:28-31. 1985.
13. Marti, C. D. and P. W. Wagner. Winter mortality in common barn owls and its effect on population density and reproduction. Condor 87:111-115. 1985.
14. Roosa, D. M. Endangered Iowa birds (an annotated list of endangered, threatened, extirpated or “status undetermined” birds of Iowa). Iowa Conserv. Comm. Spec. Rep. of Preserves Board, No. 4:12-25. 1977.
15. Schulz, T. A. Conservation and rehabilitation of the Common barn owl. Wildlife Rehabilitation. Proc. Nat. Wild. Rehab. Symp. Vol. 5:146-166. 1986.
16. Smith, D. G. and C. D. Marti. Distributional status and ecology of barn owls in Utah. Raptor Research 10(2):33-44. 1976.
17. Stewart, P. A. Dispersal, breeding, behavior and longevity of banded barn owls in North America. Auk 69:227-245. 1952.
18. Warner, R. E. and S. L. Etter. Reproduction and survival of radio-marked hen ring-necked pheasants in Illinois.J. Wildl. Manage. 47(2):369-375. 1983.
19. Wayne, A. T. A death trap to the American barn owl (Tyto pratincola). Auk 41(2):342. 1924.

TABLE 1. CAPTIVE-REARED BARN-OWLS
RELEASED 1983-1987
Year Adult Young Total

1983 12 46 58

1984 19 69 88

1985 17 82 99

1986 19 110 129

1987 6 47 53

Total 73 354 427

 

TABLE 2. CAUSES OF MORTALITY IN RADIOED
CAPTIVE-REARED BARN-OWLS
1985 1985 1986 1986 1985-86 1985-86
Cause

Avian
predation 9 64.3 4 40 13 54.2

Probable mammalian
predation 0 0 2 20 2 8.3

Auto collision 3 21.4 1 10 4 16.7

Unknown 2 14.3 3 30 5 20.8

Totals 14 100 10 100 24 100

Figure 1: Number of captive-reared barn-owls released in each of 28 counties were 427, released at 44 release sites from 1983-87’.

Figure 2: Barn-owl telemetry release sites.

Figure 3: Radioed, captive-reared barn-owl movements during 1985 and 1986 at least 30 days post-release.

Figure 4: Barn-owl movement from band returns from 1982-1987.

Figure 5: Number of verified barn-owl sightings in 50 of 99 counties where 171 were seen from 1983-1987.

Figure 6: 7 confirmed barn-owl nests in 5 counties from 1983-1987.

Published in Proceedings at the National Wildlife Rehabilitation Symposium—1984.

Common Barn-Owl Restoration in Iowa

By  Bruce L. Ehresman

Common Barn-Owl Restoration in Iowa

Bruce L. Ehresman

Iowa Conservation Commission, Wildlife Research Station

Boone, IA  50036

Abstract:  One goal of the Iowa Conservation Commission’s Nongame Program is to increase the population of the Common Barn-owl, an Iowa endangered species. Reasons for restoration include its economic value as a destroyer of grain-eating rodents, its aesthetic value to humans, and publicity for the Nongame Program.

The Iowa Conservation Commission acquires barn-owls used for restoration from other rehabilitation centers and zoos in coastal states where the owls are abundant. We use these owls either for captive breeding at the Wildlife Research Station near Boone, or for placement at selected release sites, primarily in southern Iowa. We choose release sites from areas volunteered by the public, using evaluation criteria we developed. At each release site, commission personnel enclose a section of a building to contain the owls for gentle release. Barn-owl nest box construction in release site areas is promoted. Nearly 40 boxes were erected in 1983. We place barn-owls as mated pairs, pairs with young, or groups of immature.

In 1983, we banded and released 12 adult and 46 immature barn-owls using gentle release methods. Media coverage of restoration efforts has resulted in strong public support, evidenced by Iowa’s income tax refund Checkoff participation.

Barn-owls released in 1983, and future releases, will augment Iowa’s remaining breeding population, and nest boxes erected will re-create needed nest sites.

The Common Barn-owl, as most birds of prey, has been persecuted since it first came into contact with humans. It has been the victim of random and injudicious shooting, trapping, and poisoning. Most tragically, its habitat, including critical nesting sites, has been destroyed because of human ignorance in the pursuit to “improve” our way of life on this planet. The Iowa Conservation Commission (ICC) has embarked on a restoration program to change this unjustified public attitude and to increase the population of the Common Barn-owl, an Iowa Endangered species (Roosa 1977).

DISTRIBUTION

The Barn-owl family, Tytonidae, has a worldwide distribution. It consists of eleven living species and approximately 35 subspecies. Only one of these subspecies, Tyto alba pratincola, is found throughout North America. Populations in the United States are chiefly coastal, decreasing northwards. The Barn-owl is considered a rare, permanent resident of Iowa. Because it is intolerant of cold climates (Bunn et al. 1982), it rarely breeds in the northern part of the state. Most recent sightings indicate it is most numerous in the grassland areas of the south and west portions of the state.

ECONOMIC VALUE

Before European settlers arrived, Barn-owls nested primarily in the hollow cavities of old sycamores and cottonwoods. With the cutting of these cavity trees, the Barn-owl adapted to the use of man-made structures for nesting. It also switched from eating mice and voles of native grasslands, to feed on the rats and mice that were attracted to stored grain on farmsteads. According to Lewis Walker (1974), a Barn-owl authority, single owls saves the State of California between $20 and $50 annually in its predation on pocket gophers, where pocket gophers and ground squirrels cause an estimated crop loss of 10% each year. Add to this its services in destroying voles and mice (its preferred prey), and these owls certainly do have a positive economic impact.

STATUS

It is unfortunate that a species so beneficial to humans is becoming so rare in the Midwest. Presently, the Barn-owl is listed as Endangered not only in Iowa, but also in Missouri (Wadell and Crawford 1982), Illinois (Becker 1978), and Wisconsin (Petersen 1979), and is considered threatened in Michigan (Taylor 1978).

LIMITING FACTORS

Decline of the Barn-owl can probably be attributed to a combination of factors, some interrelated. Loss of habitat, especially loss of nest sites, may be an especially important factor. Farmers have bulldozed vacant farm buildings and old hollow trees that once provided nest and roost sites, to prepare more land on which to grow cash grain crops. Modern clean-farming practices and the elimination of hay and pasture ground, prevalent on farms as recently as the mid 1960’s, has reduced habitat of the Barn-owl’s small-mammal prey.

Pesticide and rodenticide use undoubtedly have negative effects on the predator Barn-owl. Use of pesticides, particularly the chlorinated hydrocarbons, was probably most detrimental to Barn-owl populations 15 to 20 years ago before stringent regulations banned, or at least regulated their use (Bunn et al. 1982).

In Iowa, there are at least two predators that exploit the Barn-owl. Raccoons inhabiting old farm buildings harass and predate nesting Barn-owls. In the past few decades, raccoon numbers have increased in Iowa (Andrews et al. 1982) and adjoining states such as Wisconsin (Petersen 1979b). Competition with and predation by Great Horned Owls may also be a limiting factor (Wayne 1924).

Certainly collisions with automobiles, trains, power lines, etc., take a toll on Iowa’s Barn-owl population. From 1981 to 1983, 4 of 6 reported Barn-owl mortalities in Iowa were attributed to collisions.

Severe winter weather also affects survival of Barn-owls. Stewart (1952) indicated Barn-owl survival in its northern range was more influenced by snow cover amount than low temperatures. Petersen (1979a) found that snow cover depth of 10 cm or more provided cover for small mammals and protected them from owl predation in southern Wisconsin, which corresponds in latitude to northern  Iowa. Since the Barn-owl maintains the lowest body fat reserves (5.5%) of all owls examined by Piechocki (1960), it seems likely the Barn-owl cannot survive more than 3 to 4 days without feeding (Stewart 1952), especially during periods of sub-zero temperatures. Two of 4 wild Barn-owl mortalities reported in Iowa in 1983 were attributed to starvation during severe winter weather.

RESTORATION

1. States of Development

Since Iowa’s Barn-owl has been decreasing for several decades, and since the Barn-owl breeds readily in captivity, recommendations were made by Iowa’s State Ecologist, Dean Roosa (1977), to embark on a captive breeding and restoration program. Common Barn-owl restoration in Iowa began as an offshoot of the ICC’s raptor rehabilitation project at the Wildlife Research Station (WRS) near Boone. From 1960 top 1980, the facilities were used to hold birds and mammals for the state Wildlife Exhibit. Funding provided by hunting and fishing license fees allowed a wildlife rehabilitation project to begin in the late 1970’s, when Iowa’s first nongame biologist was hired. A reduction in State expenditures forced the closure of the Wildlife Exhibit in 1980.

Raptor rehabilitation at the WRS still continues, but since the fall of 1982, our main emphasis is on captive breeding, rehabilitation, and restoration of the Common Barn-owl. Reasons for restoration include its economic value as a destroyer of grain-eating rodents, its aesthetic value to humans, and publicity for the Nongame Program. Funding is now derived from an Iowa income tax refund Checkoff initiated in tax-year 1982 for Iowa’s Nongame Program.

B.    Source

Since it was virtually impossible to locate native Barn-owls for captive breeding, we had to look to outside sources. We contacted successful breeders mentioned in International Zoo Yearbooks, and publicized our project in several veterinary journals and magazines. Response was good. So far, we have received Barn-owls by air-freight shipment from rehabilitation centers in zoos in Washington, Oregon, California, Louisiana, and South Carolina. We paid air-freight costs, and during 1982-83 we received 71 Barn-owls at an average cost of about $13 per owl. We use these owls either for captive breeding at WRS facilities or for placement at selected release sites.

C.    Housing

Housing facilities at the WRS include a 14’x80’ wooden building divided into 8, 10’x7’8’ (LWH) and 4, 10’x4’x8’ pens, and a 40’x60’ steel shed containing 8, 8’x7’x8’ breeding pens connected to exterior 20’x8’x8’ flight chambers. Pens are wood framed, with walls of corrugated fiberglass panels and olefin netting. Most pens are visually separated by solid partitions to allow breeding Barn-owl pairs privacy. We place nest boxes in each pen, as well as various diameter tree branch perches. Metal flashing or smooth fiberglass skirting, two feet height, placed around the perimeter of each pen retains live mice for the owls to prey upon. Small pea gravel covers floors to facilitate cleaning. We clean pens about every three weeks, except when hens need minimum disturbance during nesting.

D.    Feeding

The diet and health of captive Barn-owls requires continuous attention. We feed routinely six days a week and fast one. Food is placed on wooden pallets, and uneaten food is removed daily. During winter months, heated food trays, modeled after those of Katherine McKeever (1979), keep the owls’ meals from freezing. We disinfect feeding pallets periodically to ensure harmful microorganisms are not transmitted to or between the owls.

Diet consists of a prepared Birds of Prey diet[1], day-old cockerel chicks culled from a local hatchery, and laboratory mice acquired from the National Animal Disease Center and Iowa State Diagnostic Laboratory in Ames. We feed these three different food items on a rotational basis to assure a balanced diet for the owls. Day-old chicks, deficient in calcium, are powdered with bonemeal before begin fed, and other supplemental minerals and vitamins are added to the diet when necessary.

E.    Medical

We treat sick or injured birds according to recommendations made at the Iowa State University’s College of Veterinary Medicine in Ames. They provide treatment and diagnoses at a teaching discount, since we provide some hands-on experience with wildlife species for students training at the clinic. We also isolate new birds brought into the facility to prevent the introduction of pathogenic organisms to or from other birds. Our personnel keep records on each owl’s health and history.

F.     Captive breeding

The ICC hopes to increase wild Barn-owl populations by releasing breeding pairs with young, and fledglings from other rehabilitators, as well as from our captive breeding pairs. All owls received from other sources are at least temporarily held at WRS facilities. Permanent cripples, human imprints, and owls that have been held several years in captivity comprise most of our captive breeders. We pair the owls for breeding according to size, temperament, age, and body condition; and place them together using methods suggested by McKeever (1979). Owls of similar sizes and temperament are our most successful breeders.

G.    Release site suitability

Before Barn-owls can be placed, release sites must be selected. We choose release sites primarily from areas volunteered by the public. After reading about this project in the newspaper, cooperators, who feel they have adequate hack sites and are willing to feed captive Barn-owls, notify Iowa’s nongame biologist. We send volunteers a “Barn-owl Release Site Preliminary Evaluation” form to complete and return. They complete this form with an aerial photograph of the proposed site, obtained from their local ASCS office. We evaluate and rate each returned form and choose release sites from those forms indicating the best habitat for Barn-owls.

Evaluation of the proposed release site includes the area within a one-mile radius of the release site structure (roughly 2,000 acres), based on the owls’ hunting behavior. The release site structure must be undisturbed, and able to be made “owl tight” with a few hours’ work. Criteria for choosing a release site are as follows:

Positive aspects –

(1)   Abundant grassland (pasture, hayfields, waterways, roadsides)

(2)   Timber in large, continuous tracts (if present)

(3)   Several people willing to feed and care for owls

(4)   Other undisturbed nest sites available nearby

Negative aspects –

(1)   Large amounts of cash grain crops

(2)   Resident Great Horned Owls present

(3)   Nearby use of rodenticides

Basically, we are looking for areas with a large proportion of permanent grassland, which have several undisturbed potential nesting sites (Bunn et. Al. 1982), and few Great Horned Owls present. Dense grasses provide good habitat for small mammals which the Barn-owl prefers as prey. Old vacant buildings or large hollow trees provide adequate nest sites. Since Great Horned Owls have been known to prey upon Barn-owls, we prefer to release our owls where such predators are not numerous. Most release sites are in areas where Barn-owls are present, or were present, within the last 5 to 20 years.

H.    Release site preparation

Once a release site with a suitable confinement structure is selected, the site must be prepared for the owls. Ideally, we prefer to allow confined owls an entire building or silo in which to fly about. This is not always possible. Usually, we are at least able to allow the owls the freedom of an entire barn loft. We close all exits, using boards or olefin netting. We then line a 16-inch square nest box, with a six-inch diameter entrance hole, with two inches of wood chips, since Barn-owls are not known to construct nests. Next, we attach this box near the top of each structure in a place that is as nearly predator-proof as possible. In silos, we place the nest box approximately two-thirds of the height above the floor (Marti et al. 1979). We supply large stock tanks to the enclosures containing fledgling owls. Live mice released into these tanks allow young Barn-owls the opportunity to learn to catch their prey before release to the wild.

I.     Placement

Barn-owls released in 1983 were placed as mated pairs, pairs with young, and groups of immature. We supplied cooperators with meat to feed the owls, and they fed the confined owls daily and monitored food consumption. Cooperators continued to feed the owls after their release until the birds were self-sufficient.

In 1983, we place 4 mated pairs (normally second-year owls) at release sites, prior to the main breeding season. In our captive Barn-owls, this has been from January through March. The hen from one pair appeared to be nesting in hay on the barn floor when she was not seen for several weeks. Since the paid did not nest successfully, and because cooperators could not fee the owls through the winter months, the pair was captured and returned to the WRS facilities prior to winter. A second pair remained captive for almost an entire year and just recently began courtship. Two captive pairs did nest after 2 months and 5 months, respectively, and fledged 5 young each. We released one of these pairs with young, but held captive the second pair with young over winter. Since these young fledged in late fall, we felt gentle release in early spring, rather than winter, would increase their survival chances. Normally, when the owlets fledge and catch live mice proficiently from the stock tank, it is time for gentle release. We open the structure so the occupants can hunt natural prey in the area near the release site. By allowing the owls to raise young at a site, we hope a bond will be established, so that either the nesting pair or their young will return to nest again in the future.

A second method of placement, which we feel is successful, is placing pairs with young. This method works well at sites where cooperators do not wish to feed captive owls daily for more than 2 or 3 months. During 1983, 5 Barn-owl pairs were placed with their 176, 3- to 4-week old young, which they hatched at the WRS.

Originally, we intended to allow parent owls freedom to hunt for natural prey outside the structure when the young are about one month old. Theoretically, the presence of the young will draw the adults back to the barn. Jane Ratcliffe (1979, cited by Bunn et al. 1982) of England, experienced good success using this method with Barn-owls. Unfortunately, the first time we tried this strategy, both adults vacated and did not return to feed their young. Our cooperator was then faced with the problem of feeding 5 very hungry owlets. It should be mentioned that we tried this method with a pair of Barn-owls and young that we moved to the site only several weeks before. With the remaining pairs, we used the same release techniques described for mated pairs – waiting until the young fledged before allowing freedom for the entire family unit. In 4 cases, this included foster young.

When the owlets of 4 family units were 6 to 8 weeks old, we added 8 more young of the same age to the broods, 2 owlets to each foster family. Four of these were WRS hatchlings, and 4 were from California. We experienced no problems with fostering young, as long as all young involved were nearly the same age.

Besides the Barn-owl family units, immature Barn-owls were also gently released. We held these owls captive at the release site for only 4 to 5 weeks. They were WRS fledglings and young owls received from California and Louisiana. To discourage inbreeding, we placed Barn-owls of different parentage at release sites of close proximity (40 miles). Volunteers hacked 4 immature owls at each of 4 sites.

In 1983, a total of 12 adult and 46 immature Common Barn-owls were banded with lock-on U.S. Fisheries and Wildlife Service leg bands and gently released. We hope this number of released owls is significant enough to have beneficial effects on the future Iowa wild breeding population. Our goals will be met when we know of at least 5 self-sustaining Barn-owl populations in Iowa habitats.

J.     Follow-up

We feel it is important to monitor the Barn-owls, even after release. Post-release monitoring is presently conducted primarily by volunteer cooperators. We ask these cooperators to keep records of post-release activity, including feeding and artificial nest box use. To ensure released owls of other roost and nest sites, at least one other nest box is erected in a vacant or little-used structure within a one-mile radius of the release site. As many as 10 nest boxes have been constructed and put up by concerned citizens in any one release site area. During 1983, nearly 40 nest boxes were erected in release site vicinities. Because our Nongame staff lacks time and manpower to monitor every nest box placed, we do appreciate the release site cooperators, County Conservation Board members, and other ICC personnel who voluntarily monitor nest box use.

Since loss of suitable nest sites is a factor in the decline of the Common Barn-owl, the ICC is promoting the use of artificial nest structures to increase our wild population. In Utah, 30 nest boxes were used by 24 barn-owl pairs to produce 154 young in 2 years (Marti et ala. 1979). We make available to the public Barn-owl life history brochures which include nest box construction and erection instructions. Many citizens have already used these instructions to build and place nest boxes.

K.    Media coverage

Media coverage at Barn-owl placement sites and about the Barn-owl restoration program has been instrumental in educating the public, as well as generating public support. Major Iowa newspaper and television stations have sent personnel to do stories at release sites with very short notice from us. Local newspaper coverage of releases has also been excellent. A number of radio stations have interviewed ICC personnel about the program. Such coverage has promoted statewide response from citizens who want to become involved with the Barn-owl restoration program. Undoubtedly it has also increased donations to the Nongame Iowa income tax refund Checkoff which funds our program.

FUTURE

Plans for 1984 include placement of 7 Barn-owl breeding pairs in January, several pairs with young in April, and approximately 20 fledglings during summer. Also, in 1984, we hope to place radio transmitters on 3 breeding pairs and 10 fledgling Barn-owls to monitor habitat use, early dispersal movements, and mortality. A graduate student from Iowa State University will be involved full time on this aspect of the program.

CONCLUSION

The success of Iowa’s Common Barn-owl restoration program is greatly dependent on public education and involvement. Much public interest has already been generated, and we need to channel this interest into involvement with building and erecting nest boxes, as well as monitoring these boxes for Barn-owl use.

It is also important that we cooperate with Barn-owl restoration projects in neighboring states such as Missouri and Nebraska. We can learn from each other’s failures and successes, and it is probably only a matter of time before a Barn-owl banded in Iowa shows up in a nest box in Missouri, or vice versa. Cooperation is certainly the key to this program’s success!

ACKNOWLEDGEMENTS

I thank Iowa’s Nongame Biologist, D. A. Newhouse, who initiated the Barn-owl restoration program, and who provided assistance in the final draft of this manuscript. I extend special thanks to my wife, M. Ehresman for being the main editor of this paper as well as providing field assistance and constant moral support. I thank S. Monen for typing this manuscript and for her secretarial work related to the restoration project. I also thank L. Crim and R. Dietz for their field assistance and dedicated care of captive breeding owls. I am grateful to Dallas Center Hy-Line International, the National Animal Disease Center and Iowa State Diagnostic Laboratory, located in Ames, for contributing their excess chicks and mice to supplement our captive owl food source; and I thank R. Lindahl and G. Crim for providing laboratory mice delivery service. I am especially thankful to the following cooperators who provided release sites and/or captive owl care, and whose efforts made Barn-owl releases possible: B. and N. Bakehouse, R. and F. Cooper, C. and K. Froyen, L. and M. Hardin, I. Hardt, C. Hensley and Cass County Conservation Board staff, L. and C. Inman, H. Jensen, L. and N. Link, M. Moe, J. and B. Sabin, E. and M. Schlueter, and B. and J. Wilson. Also, a special thanks goes to R. Minthorn who contributed 10 nest boxes for owls released in Mills County. Finally, I wish to thank the people who have contributed to Iowa’s Nongame income tax refund Checkoff, which funds this project.

LITERATURE CITED

ANDREWS, R. D., J. L. HANSEN, and B. R. OHDE. 1982. Furbearer harvest survey. Iowa Conserv. Comm. Study no. 19.

BECKER, C. 1978. Endangered and threatened wildlife. Ill. Dept. Conserv. 1-4.

BUNN, D. S., A. B. WARBURTON, and R. D. S. WILSON. 1982. The Barn Owl. Vermillion, South Dakota, Buteo Books.

MARTI, C. D., P. W. Wagner, and K. W. DENNE. 1979. Nest boxes for the management of barn owls. Wildl. Soc. Bull. 7(3):145-148.

MC KEEVER, K. 1979. Care and rehabilitation of injured owls. Ontario, Canada, W. F. Rannie.

PETERSEN, L. R. 1979a. Ecology of Great Horned Owls and Red-tailed Hawks in Wisconsin. Wis. Dept. Nat. Resour. Tech. Bull 111:1-95.

_______. 1979b. Status of Barn Owls in Wisconsin. Wis. Dept. Nat. Res. Rep. 1097:1-11.

PIECHOCKI, R. 1960. Uber die winterverluste der schleiereule. (Tyto alba). Vogelwarte 20:274-280.

RATCLIFFE, E. J. 1979. Fly high, run free. London.  Reference not available, cited from Bunn et al. (1982)

ROOSA, D. M. 1977. Endangered Iowa birds (an annotated list of endangered, threatened, extirpated or “status undetermined” birds of Iowa). Iowa Conserv. Comm. Spec. Rep. of Preserves Board, no. 4:1-25.

STEWART, P. A. 1952. Dispersal, breeding behavior, and longevity of banded Barn Owls in North America. Auk 69:227-45.

TAYLOR, S. M. 1978. Michigan’s endangered and threatened species program. Mich. Dept. Nat. Resour. 1-35.

WADDELL, W., and W. C. CRAWFORD, Jr., 1982. Barn Owl recovery program – Missouri and the Midwest. Pp. 74-80 in wildlife rehabilitation (P. Beaver, ed.). Smithtown, New York, Exposition Press, Inc.

WALKER, L. W. 1974. The book of owls. New York, Alfred A. Knopf, Inc.

WAYNE, A. T. 1924. A death trap to the American Barn Owl (Tyto pratincola). Auk 41(2):342.

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[1] (Product of Central Nebraska Packing Company of North Platte. Mention of trade names does not imply endorsement by the ICC.)